In sociological terms, a social network is formed of a collection of people who have social connections with each other. In recent years, computerized social networking services have emerged to facilitate the building of social networks and to host electronic interactions between members of social networks. Typically, each user registered with a computerized social networking service creates an online representation of him/herself, called a “profile,” that contains biographical and other information about the user. The user then creates an online representation of his/her social network by declaring connections with other users registered with the social networking service. For example, a first user might declare a connection with a second user by designating the second user as a “friend” or a “contact,” or by choosing to “follow” the second user on the computerized social networking system. The first user's profile maintained by the social networking system often includes a list of other users who are “friends” or “contacts” of the first user, or whom the first user is “following.” Often the social networking service imposes a requirement that both users must declare a mutual connection before the connection will be recognized and listed on the users' profiles, or before it will be publicized to other users. For example, when the first user designates the second user as a “friend,” the second user may be required to accept the first user's “friend” request before the two users will be listed online as “friends.” Declared connections can also later be undeclared, severing the link between the users' online profiles. For example, a first user who is a “contact” of a second user might later undeclare the connection by indicating that the second user is no longer a “contact,” with the result that each user is then removed from the list of the other user's “contacts” on the other user's profile.
Social network analysis applies network theory to the sociological study of social networks. A typical social network can be represented graphically as a collection of nodes and edges. As applied to a computerized social networking service, each node in the network analysis graph can represent a user with a profile registered with the online social networking system. Each edge connecting two nodes in the graph can represent a declared connection between the two users represented by the two nodes. Such network graphs have been used as tools for the visualization of social networks, to allow an observer or researcher to get a sense of the network's overall structure formed by the connections between and among its members.